The nose section of aircraft has been subject to many developments seeking to optimise its mass, volume, cost, safety, ease of manufacture and maintenance, etc. Such a nose section is known, for example, from documents FR 2 910 875 and U.S. Pat. No. 7,784,736.
Despite the existence of many embodiments, it is desirable to reduce further the volume of the landing gear compartment of the nose section.
The volume of a landing gear compartment is determined notably by the compactness of the landing gear in its raised state, which compactness depends notably on the geometry of the breaker strut of the landing gear. Such a breaker strut is a well-known element intended to stabilise the landing gear in its lowered state.
As illustrated by FIGS. 1 to 4, which partially represent a landing gear 10 of a known type, breaker strut 12 is generally formed from two portions, the lower one of which 14 includes first means 16 of articulated connection to undercarriage 18 of the landing gear by a first hinge axis 20, and the upper one of which 22 includes first means 24 of articulated connection to the aircraft by a second hinge axis 26. These two strut portions are connected to one another along a third hinge axis 28 which is parallel to abovementioned lines 20 and 26. Both portions 14 and 22 can thus be moved relative to one another between a deployed position (FIG. 2), in which lower portion 14 is positioned facing upper portion 22 relative to abovementioned third line 28, and in which first line 20 is roughly contained in a plane defined by second line 26 and third line 28, and a folded position (FIGS. 3 and 4), in which lower portion 14 is folded towards a lower face 30 of upper portion 22. It should be noted that FIG. 1 illustrates both raised state, 54, and lowered state, 52, of landing gear 10.
Lower portion 14 is generally formed from a connecting rod, whereas upper portion 22 is formed from an A-shaped structure, the apex of which includes a fork joint 32, in which an upper end 34 of lower portion 14 is connected in articulated fashion (FIG. 2). This structure includes two oblique arms 36, each of which has a lower end 38 connected to fork joint 32 and a facing end 40 having a sleeve 42 forming part of first means 24 of articulated connection of upper portion 32. In addition it is preferable, for reasons of rigidity, that both oblique arms 36 should be connected to one another by a transverse arm 44 close to their respective ends 40 having abovementioned first means 24 of articulated connection.
The compactness of breaker strut 12 in its folded position depends essentially on angle α between planes PS1 and PI1 in which the upper portion 22 and lower portion 14 are contained respectively in the folded position (FIG. 1), and on angle β between plane PS2 in which upper portion 22 is contained in the deployed position, and plane PS1 in which this upper portion 22 is contained in the folded position. The compactness of the breaker strut 12 in the folded position also depends on the ratio of the respective lengths LI and LS of the lower portion 14 and upper portion 22. It should be noted that the plane in which lower portion 14 is contained is defined as the plane containing first hinge axis 20 and third hinge axis 28, whereas the plane in which upper portion 22 is contained is defined as the plane containing second hinge axis 26 and third hinge axis 28.
And, as FIG. 4 illustrates more clearly, angle α between lower portion 14 and upper portion 22 in the folded position is limited by fork joint 32 to a minimum value which is typically equal to approximately 20 degrees. Generally, abovementioned angle α can be limited not only by fork joint 32, but also by the risk of a collision between upper portion 22 and leg 46 of undercarriage 18 in the raised state of undercarriage 10. As is shown by FIG. 3, this risk of collision concerns in particular transverse arm 44 and the region of mutual connection of both oblique arms 36 of upper portion 22.
Angle β between plane PS1 and plane PS2, and also respective lengths LI and LS of lower portion 14 and upper portion 22, are determined so as to allow a control linkage of the landing gear which has no locking points. Such a constraint habitually imposes minimum values respectively for angle β and for length LS of upper portion 22.
Furthermore, the volume of a landing gear compartment is also determined by the compactness of the landing gear retraction means. Retraction means must be understood to mean the mechanism enabling the undercarriage to be raised from its lowered state to its raised state.
FIG. 5 illustrates in a very simplified manner a nose section 48 of a conventional aircraft, and more specifically compartment 50 of forward landing gear 10, together with undercarriage 18 of this gear in its lowered state 52 and raised state 54, and in an intermediate state 53.
As it is raised, undercarriage 18 is made to rotate around its pivot axis 56, and is subjected principally to two moments which are combined, but which change in opposition to one another. The first moment results from the weight of the undercarriage, applied to its centre of gravity 58, and represented symbolically by arrow 60, and from corresponding leverage 62. The second moment results from the effects 64 of the relative wind, which essentially affects wheel 66 of undercarriage 18, and from corresponding leverage 68. It should be noted that in FIG. 5 weight 60, force 64 due to the relative wind and associated leverages 62 and 68 are represented only for the intermediate state of landing gear 10.
In lowered state 52 the second moment due to the relative wind is at its maximum due to corresponding large leverage 68, whereas the first moment associated with the weight is zero. Conversely, in raised state 54 the first moment associated with the weight is at its maximum due to corresponding large leverage 62, whereas the second moment due to the relative wind is zero. Between these two states the two moments change in opposition to one another, and producing a combined effect, such that the total moment applied to the undercarriage is roughly constant as it moves.
FIG. 5 also illustrates the retracting means of gear 10, which operate according to a slider-crank mechanism including a crank 70 coupled to leg 46 of undercarriage 18, together with a linear actuator 72 which includes a rod 74 coupled to crank 70, and a cylinder 76 connected to roof 78 of gear compartment 50.
FIGS. 6a, 6b and 6c illustrate the abovementioned retraction means at a larger scale, and correspond respectively to the raised, intermediate and lowered states of landing gear 10.
As is clear from these FIGS. 6a to 6c, the retraction torque of undercarriage 18 varies as the undercarriage rotates. This torque is, indeed, equal to the product of the generally constant force of the actuator, represented symbolically by arrow 80, and the variable associated leverage represented symbolically by arrow 82. More specifically, this retraction torque is minimal in the extreme positions corresponding to the raised and lowered states of the gear illustrated by FIGS. 6a and 6c respectively, and this torque is highest in the intermediate position of FIG. 6b. 
As a consequence, this configuration of the retraction means does not appear to be optimal, bearing in mind the roughly constant forces which these retraction means must oppose, as explained above. This generally leads the retraction means, and notably actuator 72, to be dimensioned such that force 80 of the latter is sufficient to exceed the forces due to the weight of the undercarriage and to the relative wind, even when leverage 82 associated with actuator 72 is minimal, i.e. in the undercarriage's raised and lowered states. This results in undesirable excess mass and cost.
In addition, as shown by FIG. 6c, rod 74 of actuator 72 comes close to pivot axis 56 of undercarriage 18 when landing gear 10 is in its lowered state. This proximity of rod 74 and pivot axis 56 is more pronounced the greater the angular displacement 6 traversed by undercarriage 18 between its raised and lowered states (FIG. 5). In practice, this results in a limitation of this angular displacement to an angle value close to approximately 105 degrees, above which value rod 74 of actuator 72 would come into collision with a pivot element of undercarriage 18.
With the aim of optimising aircraft it is generally desirable to make compartment 50 of forward landing gear 10 as close as possible to forward end 84 of the aircraft (FIG. 5). However, such proximity requires that angular displacement θ followed by undercarriage 18 between its raised and lowered states is increased above the abovementioned limiting value. This angular displacement must be increased still further when undercarriage 18 is of the retractable type, i.e. where it becomes shorter as the undercarriage is raised. This type of undercarriage is, however, of great interest in terms of increased compactness.
In addition, the roughly vertical positioning of actuator 72 has a detrimental effect on the vertical compactness of gear compartment 50.
In addition, positioning this actuator 72 in a direction close to the horizontal direction would have a detrimental effect on the lengthways compactness of gear compartment 50. Indeed, the slider-crank mechanism must not pass through a dead centre, i.e. a state in which leverage 82 associated with actuator 72 is zero as undercarriage 18 is raised, since such a situation would clearly lead the undercarriage to lock. As a consequence, in a configuration in which actuator 72 extends roughly horizontally, as illustrated in FIG. 7, crank 70 necessarily traverses a vertical plane PV passing through pivot axis 56, and continues well beyond this plane PV, requiring that the position of rear wall 86 of gear compartment 50 is moved towards the rear.